The debate is over. Over the last century, average land surface temperature has risen approximately 1.0° F, and the 10 warmest years of the 20th century all occurred within the last 15 years of the century. Why? Atmospheric concentrations of carbon dioxide, the most common greenhouse gas, are 30% higher than before the Industrial Revolution.

By far, the U.S. is the highest emitter of carbon dioxide in the world, responsible for about one-fifth of the total emissions of greenhouse gases. That equates to nearly 6.6 tons of greenhouse gases per person per year--and the per-person emissions 3.4% between 1990 and 1997.

Rising temperatures will have enormous impacts on the Earth in the future. Some estimates are that by 2100 the Earth’s land temperature will increase 2° F to 7° F. And here are some of the expected reverberations: Rising sea levels inundating coastal communities, altered crop yields and water supplies, increased floods and droughts and surges in infectious diseases.